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United States Patent |
6,039,883
|
Milde
,   et al.
|
March 21, 2000
|
Compound method for disinfection of liquids
Abstract
Various chemical disinfectants, such as chlorine, have a broad capability
for destroying or deactivating microbes, but can produce harmful
disinfection by-products. They also result in residual contamination by
the disinfecting chemical. The application of high potential gradients to
a liquid medium containing microbes also has a powerful disinfecting
action. The combination of chemical disinfectants with the electric
process leads to a compound process of great effectiveness, whereby the
electrical process acts with greater efficiency and the amounts of
chemical disinfectant required are substantially reduced.
Inventors:
|
Milde; Helmut I (Boxford, MA);
Philp; Sanborn F (Pittsfield, MA)
|
Assignee:
|
Ion Physics Corporation (Atkinson, NH)
|
Appl. No.:
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983533 |
Filed:
|
January 7, 1998 |
PCT Filed:
|
July 25, 1996
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PCT NO:
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PCT/US96/12174
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371 Date:
|
January 7, 1998
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102(e) Date:
|
January 7, 1998
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PCT PUB.NO.:
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WO97/05067 |
PCT PUB. Date:
|
February 13, 1997 |
Current U.S. Class: |
210/748; 205/701; 205/742 |
Intern'l Class: |
C02F 001/461; A61L 002/02 |
Field of Search: |
205/701,742
204/272
210/748,754,764
|
References Cited
U.S. Patent Documents
4384943 | May., 1983 | Stoner et al. | 204/149.
|
4492618 | Jan., 1985 | Eder | 204/152.
|
4769119 | Sep., 1988 | Grundler | 204/149.
|
5048404 | Sep., 1991 | Bushnell et al. | 99/451.
|
5130032 | Jul., 1992 | Sartori | 210/748.
|
5235905 | Aug., 1993 | Bushnell et al. | 99/451.
|
5326530 | Jul., 1994 | Bridges | 422/22.
|
Foreign Patent Documents |
22089 | Sep., 1972 | DE | 204/272.
|
WO 83/02215 | Jul., 1983 | WO | 210/748.
|
Other References
Dec.1990 IEEE Industry Applications Meeting 1712 90.
Copy of the International Search Report dated Jan. 8, 1997.
|
Primary Examiner: Simmons; David A.
Assistant Examiner: Lawrence; Frank M.
Attorney, Agent or Firm: Nields, Lemack & Dingman
Parent Case Text
This application is a nonprovisional filing of U.S. provisional patent
application Ser. No. 60/001,552 filed Jul. 27, 1995, now abandoned.
Claims
We claim:
1. A process for disinfection of liquids comprising the following steps:
placing the contaminated liquid to be disinfected in an E-field processing
chamber containing electrodes,
applying at least one voltage pulse across said electrodes of sufficient
magnitude and number to have a disinfecting action on said liquid, and
adding to said liquid a disinfectant capable of increasing said
disinfecting action produced by said voltage.
2. A process according to claim 1, wherein the contaminated liquid is
placed in the processing chamber as a flowing stream of liquid.
3. A process according to claim 1, wherein the contaminated liquid is
placed in the processing chamber as a given volume of liquid (a "batch")
and not as a flowing stream of liquid; and to this batch of liquid said
substance is added according to one or more of the following: (a) before,
(b) during, or (c) after the E-field process.
4. A process according to claim 1, wherein the applied voltage and the
geometry of the chamber and electrodes are such that a potential gradient
of at least 1000 V/cm is produced within the liquid.
5. A process according to claim 1, wherein the pulses have a duration in
time of one millisecond, or less, and are repeated at a rate of at least
one pulse per second.
6. A process according to claim 1, wherein the potential gradient is
produced by electrodes of shapes which result in a potential distribution
which is uniform.
7. A process according to claim 1, wherein the potential gradient is
produced by electrodes of shapes which result in a potential distribution
which is approximately uniform--as in concentric cylindrical electrodes.
8. A process according to claim 1, wherein the potential gradient is
produced by electrodes of shapes, which result in a potential distribution
which is non-uniform.
9. A process according to claim 6, wherein dielectric structures are
introduced into the interelectrode gap or in the vicinity of the
interelectrode gap in order to alter the configuration of the field.
10. A process according to claim 7, wherein dielectric structures are
introduced into the interelectrode gap or in the vicinity of the
interelectrode gap in order to alter the configuration of the field.
11. A process according to claim 8, wherein dielectric structures are
introduced into the interelectrode gap or in the vicinity of the
interelectrode gap in order to alter the configuration of the field.
12. A process according to claim 2, wherein the said disinfectant is added
in one or more of the following ways: (a) introduced into a chamber
connected to, or a pipe leading to, the E-field p rocessing chamber and
preceding this processing chamber in the flow path; (b) introduced into
the E-field processing chamber itself; (c) introduced into a pipe or
chamber which lies after the E-field processing chamber in the flow path.
13. A process according to claim 1, wherein said disinfectant is added to
said liquid no later than one minute after said liquid leaves said
chamber.
14. A process according to claim 1, wherein the applied voltage and the
geometry of the chamber and electrodes are such that a potential gradient
of at least 10,000 V/cm is produced within said liquid.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the disinfection of liquids, especially those
containing microbes, and combines the use of chemical disinfectants with
the application of high potential gradients to a liquid medium containing
microbes.
2. Description of the Related Art
High potential gradients applied to a medium containing microbes can
destroy or deactivate the microbes. This has been known for at least fifty
years. Sale and Hamilton were the first to publish definitive experimental
data on this effect and to demonstrate that the effect was evidently due
to the potential gradient per se, and not the result of heating or the
passage of electric current. See, for example, A. J. H. Sale and W. A.
Hamilton, Effect of High Electric Fields on Microorganisms I. Killing of
Bacteria and Yeasts, Biochimica & Biophysica Acta 148, 781 (1967); W.
A.Hamilton and A. J. H. Sale, Effects of High Electric Fields on
Microorganisms II. Mechanism of Action of the lethal Effect, Biochimica &
Biophysica Acta 148, 789 (1967); A. J. H. Sale and W. A. Hamilton, Effect
of High Electric Fields on Microorganisms III. Lysis of Erythrocytes and
Protoplasts, Biochimica & Biophysica Acta 163, 37 (1968). Subsequent
microbiological studies by Benz and Lauger (see, for example, Roland Benz
and P. Lauger, Kinetic Analysis of Carrier-Mediated Ion Transport by the
Charge-Pulse Techniaue, Journ. Membrane Biol. 27, 171 (1976)), Zimmermann
et al. (see, for example, Ulrich Zimmermann, J. Vienken & Gunther Pilwat,
Development of drug Carrier Systems: Electrical Field-Induced Effects in
Cell Membranes, Bioelectrochem. & Bioenergetics 7, 553 (1980); Ulrich
Zimmermann, Peter Scheurich, Gunther Pilwat & Roland Benz, Cells with
Manipulated Functions: New Perspectives for Cell Biology, Medicine &
Technology, Angewandte Chemie 93, 332 (1981)), and Benz et al. (see, for
example, Roland Benz, F. Beckers & Ulrich Zimmermann, Reversible
Electrical Breakdown of Lipid Bilayer Membranes: A Charge-Pulse Relaxation
Study, Journ. Membrane Biol. 48, 181 (1979); Roland Benz & Ulrich
Zimmermann, Pulse-Length Dependence of the Electrical Breakdown in Lipid
Bilayer Membranes, Biochimica & Biophysica Acta 597, 637 (1980)), showed
that high potential gradients induce porosity in the membrane of a
biological cell. Below a certain value of applied potential gradient--this
critical value being of the order of 10 kV/cm--the induced porosity is
reversible: That is, when the gradient is removed, the membrane
regenerates its properties and the cell is not permanently affected.
Whereas, for values of gradient above the critical value, porosity rapidly
increases with increase in the applied gradient, and there is an
increasing probability that the cell will be destroyed.
Various systems for applying high potential gradients to a medium
containing microbes are disclosed in U.S. Pat. No. 5,048,404 to Bushnell
et al. and in U.S. Pat. No. 5,235,905 to Bushnell et al.
SUMMARY OF THE INVENTION
As porosity of the membrane increases, there is an increase in the exchange
of fluids between the interior of the cell and the medium which surrounds
the cell. If a chemical disinfectant is present in the medium, this
disinfectant will be carried into the cell with consequent adverse effect
on cell viability. Potential gradients, by themselves, adversely affect a
cell's viability. When the applied gradient exceeds the critical value and
irreversible changes occur, both membrane porosity and the probability
that the cell will be destroyed increase rapidly with increasing potential
gradient. For these reasons, combining the high-potential gradient process
with treatment by addition of small amounts of chemical disinfectant
results in a process of high effectiveness.
Accordingly, in accordance with the invention, the liquid, contaminated
with microbes, is contained within a processing chamber. Within this
chamber are electrodes which themselves constitute part of the envelope of
the contained volume of liquid to be processed. In this way, all fluid in
the chamber--or all fluid passing through the chamber--is subjected to the
high potential gradient, which is applied as a sequence of pulses. The
applied potential gradients have an effect on the microbes which persists
for a significant period of time after the application of the gradient has
ceased--or after the microbe has passed out of the chamber where the
gradients are applied. Even in the case of low gradients (say, of the
order of 2000 V/cm), for which the membrane-related effects--such as
porosity--are reversible, it has been shown (see hereinabove, Zimmermann,
Vienken and Pilwat, 1980) that these effects persist for several minutes,
at temperatures in the range 20.degree. C. -30.degree. C., and can persist
for times of the order of an hour at 4.degree. C. Consequently, there are
several different modes for application of chemical disinfectant to a
flowing stream of liquid which is to be disinfected by a combination of
the chemical and high potential gradients: (1) The disinfectant can be
added prior to (that is, up-stream from ) the electric field process. (2)
It can be added simultaneously with the electric field process. (3) It can
be added after (downstream from) the electric field process, provided
that, in case (3), the locus for addition of the disinfectant must be a
place in the fluid flow which the liquid would reach in less than
(roughly) one minute after exposure to the potential gradient.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may best be understood from the following detailed
description thereof, having reference to the accompanying drawings, in
which:
FIG. 1 is a somewhat diagrammatic view of the process steps of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, and first to FIG. 1 thereof, therein is shown an
apparatus for carrying out the process of this invention and intended for
the disinfection of a continuously flowing stream of liquid. This
apparatus includes a means of mixing, which incorporates a valve and
pipework, which permits a controllable stream of dilute disinfectant to
flow continuously into the volume wherein mixing with the fluid occurs.
The processing chamber contains an arrangement of electrodes such that the
liquid to be processed is subjected to an electric field resulting from a
potential difference maintained between various of these electrodes. The
liquid enters first at an inlet pipe to the means of mixing, passes
through this part of the apparatus, and then exits through a short pipe
connecting into the electric field processing chamber. Baffles are
provided in the mixing region (or the contents of the region may be
continuously stirred) and the location of inlet and outlet are such that
every element of input liquid spends a time in the mixing means which is
approximately equal to the volume of this space divided by the volumetric
rate of flow. From the mixing means, the liquid passes to the electric
field processing chamber where high voltage pulses, applied at a certain
rate across the electrodes, cause pulsed gradients to be induced in the
liquid.
In one embodiment of the present invention, dielectric structures are
introduced into the interelectrode gap or in the vicinity of the
interelectrode gap in order to alter the configuration of the field.
The effectiveness of the subject invention is exemplified by the following
experiments, in which chlorination and the pulsed gradient process are
first applied separately and then combined into a single process. In each
case, a liquid stream contaminated with coliform bacteria was passed
through the apparatus. Samples were taken from the input stream and from
the output stream for bacteriological analysis. Three different cases were
studied:
(a) No chlorine was added to the disinfecting tank and the liquid stream
was subjected only to pulsed gradients. The applied pulses produced a peak
gradient of 40 kV/cm, and the pulse repetition rate was such, in relation
to the velocity of flow , that every element of the liquid was subjected
to approximately 20 pulses.
(b) A mixing tank was filled with several gallons of contaminated liquid
and a dilute solution of hypochorite was introduced into the tank so that
the added hypochlorite was in a proportion of 1.9 parts per million to the
liquid volume in the tank. The residence time of the hypochlorite in the
tank was 10 minutes. After this period, the liquid was dechlorinated with
sodium bisulfite.
(c) The throughput liquid was subjected to both the electric field process
described in (a) and the chlorination described in (b).
The results obtained from (a), (b) and (c) are summarized in the following
Table:
______________________________________
Surviving Fraction of Microbes under Three Different
Operating Conditions
Total Fecal
coliform bacteria
coliform bacteria
______________________________________
(a) Pulsed field only
0.0037 0.0048
(b) Chlorine (Cl) only
0.027 0.023
(c) Pulsed field and Cl
less than 0.00013
less than 0.0009
______________________________________
Having thus described the principles of the invention, together with
illustrative embodiments thereof, it is to be understood that, although
specific terms are employed, they are used in a generic and descriptive
sense, and not for purposes of limitation, the scope of the invention
being set forth in the following claims.
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